Investigation of atomic structures of diamond-like amorphous carbon by electron energy loss spectroscopy

Research into amorphous carbon films has been developed to such an extent that the film property can be fine tuned to mimic that of the crystalline counterparts, be it diamond, graphite, or even fullerene-like. This flexibility makes such films ideal for a wide range of applications from anti-abrasive window coating to lubricating layers on the surface of magnetic hard-disk. Not only are their mechanical properties interesting, electrically the diamond-like amorphous carbon films are also easier to dope than crystalline diamond, making them potentially a better alternative to amorphous silicon for photovoltaic devices. We will show that electron energy loss spectroscopy, in particular the carbon 1s core absorption spectroscopy, has been instrumental in revealing the nature of the bonding between carbon atoms. Such information allows microstructure models to be developed for proper understanding of the observed properties and providing scientific basis for future improvement.

The density of electrons in a perfect or imperfect lattice

The spatial distribution of electronic charge is calculated exactly for three simple cases. These are the perfect lattice, perfect lattice with a single vacancy and perfect lattice with a single substitutional impurity. The potential is assumed to be of muffin tin form. The results are similar in appearance to the equations for the Kohn-Rostoker band structure calculations and appear ideally suited to numerical computation. Examples are given to illustrate the results. These are rather simple, but two interesting conclusions can be drawn: the charge at a vacancy is not directly proportional to the density of states of the host lattice and an impurity can cause two bound states to appear from a narrow band.

Interplay between Electronic Structure and Correlation through the s-d Mixing in Transition Metal Systems

The s-d mixing which refers to the mixing between d states of a transition element atom and states of s, p, f,… symmetries of neighboring atoms can be of primary importance even in transition metal systems. A mechanism for enhancing the ferromagnetism of iron atom systems through the s-d mixing with s, p valence atoms such as B, C and N which seems to be operating in Nd2Fe14B and other systems is discussed as an illustrative example of the static perturbation effect. A possible role of the s-d mixing in producing the discrepancies of the band structure calculation from the experimental data on single electron excitations in nickel is discussed by extending the discussion on impurities.